1. Field of the Invention
The present invention relates to a development process in a method for manufacturing a semiconductor device.
2. Description of the Background Art
In the method for manufacturing the semiconductor device, a resist pattern formation that is an important microfabrication process is composed of steps below. (1) First, a photoresist (photosensitive material) film is applied to a surface of a semiconductor substrate. (2) Next, an ultraviolet exposure device prints a circuit pattern on the photoresist film with a use of a mask. (3) Lastly, a development process of the photoresist film is performed. These three steps form a resist pattern.
The development processing steps are composed of steps below. (1) First, the photoresist film on which the circuit pattern is printed is immersed in a developing solution. (2) Next, it is immersed in a development stopping solution (rinse solution) such as pure water, and the developing solution is replaced with the rinse solution to stop development. (3) Lastly, a wafer is rotated to drain the rinse solution to dry the wafer.
In the step (1) of immersing the photoresist film in the developing solution, the semiconductor substrate is often rotated after or while dropping the developing solution on the semiconductor substrate, to spread the developing solution entirely on the semiconductor substrate. At this time of dropping the developing solution, air might be taken in. Moreover, when nitrogen and the like apply pressure to the developing solution for dropping, the developing solution dropped on the semiconductor substrate returns to the atmospheric pressure, and then the nitrogen and the like dissolved in the developing solution during pressurization are foamed. Furthermore, in a case where the photoresist film is a positive -type photoresist film including a novolak resin, the nitrogen generated by a photosensitive reaction during exposure is taken into the photoresist film. Because of the multiple factors above, microbubbles (bubbles) are generated in the developing solution dropped onto the surface of the photoresist film. Some of the microbubbles adhere to the surface of the photoresist film. The adhered microbubbles prevent the developing solution from coming in contact with the photoresist film, thereby causing development defects. Thus, efficiency percentage of the semiconductor device is reduced.
As a method of removing the microbubbles, Japanese Patent No. 3708433 (2005), Japanese Patent Application Laid-Open No. 09-244258 (1997), and Japanese Patent Application Laid-Open No. 2011-77120 disclose that discharges of the development solution divided into multiple times are effective. In the method disclosed in Japanese Patent No. 3708433 (2005), first, while the semiconductor substrate is rotated at a velocity of 100 to 500 rpm, the developing solution is dropped on the semiconductor substrate for enhancing the surface wettability of the semiconductor substrate. Next, the developing solution is stopped to drop and the semiconductor substrate is rotated at a velocity of 500 to 1500 rpm. Lastly, while making the semiconductor substrate remain at rest or rotating it at a velocity of 100 rpm or less, the developing solution is dropped again to be puddled on the semiconductor substrate. Subsequently, the rinse solution is dropped on the semiconductor substrate and the developing solution is washed out.
Also, Japanese Patent Application Laid-Open No. 09-244258 (1997) discloses that the microbubbles, which are puddled on during a discharge of the developing solution for the first time to adhere to the surface of the photoresist film, can be removed by the discharge of the developing solution on the semiconductor substrate for the second and subsequent times. After discharging the developing solution to be puddled on the semiconductor substrate, the semiconductor substrate repeats high acceleration rotations and stops, whereby the microbubbles can also be removed.
Also, Japanese Patent Application Laid-Open No. 2011-77120 discloses the method of discharging the developing solution on the photoresist film again with an interval of the predetermined time after discharging the developing solution on the photoresist film. The second developing solution has a lower concentration than the first developing solution, so that the development is less advanced in the first development process than the second development process. Thus, the microbubbles can be removed effectively.
In the methods of Japanese Patent No. 3708433 (2005), Japanese Patent Application Laid-Open No. 09-244258 (1997), and Japanese Patent Application Laid-Open No. 2011-77120, the developing solution is discharged multiple times or the semiconductor substrate is rotated after the discharge of the developing solution, in order to move the microbubbles in contact with the surface of the photoresist film. These methods are capable of reducing the development defects caused by the microbubbles. However, it is required to reduce or eliminate the development defects more stably.
According to the method of Japanese Patent Application Laid-Open No. 2011-77120, it is necessary to prepare a plurality of developing solutions having various concentrations for a developing device, thereby increasing costs.